Response of phytoplankton and bacterial biomass during a wastewater effluent diversion into nearshore coastal waters

Abstract

A 3-week diversion of the Orange County Sanitation District effluent discharge into nearshore waters off Newport Beach, CA constituted a considerable injection of secondarily-treated effluent into the coastal ecosystem. Thelocation 1.6 km from shore, shallow water de m),volume and nutrient content 8 liters day-1 of effluent with inorganic nitrogenconcentration>2 mM) during the diversionraised concerns regarding the potential for stimulating phytoplankton blooms and, in particular, blooms of toxic species. Remarkably, phytoplankton standing stocksduring the event and shortly thereafter did not reachvalues associated even withminor blooms historically observedin the region (generally <5 g l-1), although shifts in community compositionwere observed. Diatom abundances increased early during the diversion, dinoflagellates,phototrophic picoplanktonic eukaryotes and other algae increased mid-diversion, and cyanobacteria (Synechococcus, Prochlorococcus) increased near the end of the diversion. Concentrations of domoic acid(a phycotoxin commonly present in the area) remained near or below detectionthroughout the diversion, and abundances of potentially-harmful algal species were unresponsive. Bacterial biomass increased during the diversion, and equaled or exceeded total phytoplankton biomass in most samples.Abundances of microbial grazerswere also elevatedduring the diversion. We speculate that nutrient uptake by the bacterial biomass, acting in concert with or a response to a negative effect of disinfection byproducts associated with chlorination on phytoplankton physiology, played a significant role in muting the response of the phytoplankton to nutrients released in the effluent.

Seasonal and Temporal Drivers Influencing Phytoplankton Community in Kuwait Marine Waters: Documenting a Changing Landscape in the Gulf

“…These environmental changes have been related to several incidents of algal blooms, HABs, and fish-kills (Heil et al, 2001;Gilbert et al, 2002;Al-Yamani et al, 2004;Sheppard et al, 2010;Al Shehhi et al, 2014). The primary form of nitrogen can differ depending on the pressures and can influence the plankton species (Howard et al, 2007) with growth rate and proliferation of HAB species varying with the nitrogen source (Thessen et al, 2009;Caron et al, 2017;Glibert, 2017;Seubert et al, 2017). Depending on the species and scale, phytoplankton blooms can have significant impacts locally or over wider areas.…”

Application of Landsat 8 for Monitoring Impacts of Wastewater Discharge on Coastal Water Quality

“…Wastewater effluent has been found to contribute as much nitrogen to coastal regions as wind-driven upwelling in several sub-regions of the Southern California Bight, including Santa Monica Bay, thereby doubling the nitrogen load (Howard et al, 2014;McLaughlin et al, 2017). A primary environmental concern of the release of nutrient-rich wastewater into the Southern California Bight is the stimulation of primary production, which can lead to eutrophication and the proliferation of toxic harmful algal blooms (Caron et al, 2017). Under typical density-stratification conditions for the region, the discharge of wastewater near the head of the Santa Monica Submarine Canyon (8.1 km offshore at 57 m depth), limits the likelihood that wastewater will surface and affect marine life and human health (Washburn et al, 1992;Uchiyama et al, 2014).…”

“…The cold SST anomaly provides a physical indicator of whether or not the discharged wastewater has risen to the surface and provides some indication of its transport direction. The surfacing wastewater introduces excess nutrients, mainly ammonium, to the euphotic zone, where it has been shown to stimulate phytoplankton growth and production in the region (Reifel et al, 2013;Howard et al, 2014;Caron et al, 2017;Gierach et al, 2017).…”

“…In contrast, the 1-mile outfall pipe terminates within the shallow nearshore region of Santa Monica Bay, discharging the wastewater at 18 m depth. During diversion events, the discharge of wastewater through the 1-mile outfall pipe increases contaminant and nitrogen concentrations in the shallow and sunlit coastal waters of Santa Monica Bay, thereby increasing the probability of phytoplankton blooms and contaminant exposure to marine life and humans, as Santa Monica Bay is a major coastal recreation area (Caron et al, 2017;Gierach et al, 2017).…”

Evaluation of uptake kinetics during a wastewater diversion into nearshore coastal waters in southern California

“…The ambient nutrient concentrations collected simultaneously with experiment water are provided in Table 1. Nitrate was below 0.5 μM N, ammonium below 0.25 μM N and urea below 0.7 μM N. The chl a concentrations collected from the experiment water were low pre-diversion (1.0 μg L -1 ), and increased to 3.5 μg L -1 during the diversion, which is relatively low for the San Pedro area (Seubert et al 2013;Seegers et al 2015;Caron et al,…”